Air batteries are nonaqueous batteries using air as a positive-electrode active material, and they have a relatively high energy density and are easy to be made small in size and light in weight, which are desirable. When metal Li is used as a negative-electrode active material of such an air battery, the following reactions (1) to (4) occur.    DISCHARGED STATENEGATIVE ELECTRODE: 2Li→2Li++2e−  (1)AIR ELECTRODE: 2Li++2e−+O2→Li2O2  (2)            SOME AMOUNT OF Li2O MAY BE GENERATED.            CHARGED STATENEGATIVE ELECTRODE: 2Li++2e−→2Li  (3)AIR ELECTRODE: Li2O2→2Li++2e−+O2  (4)
Air batteries are structured to take in oxygen from the outside and thus they usually have porous membranes having a high oxygen permeability. However, in the case of such open-type air batteries, the moisture in the air is also drawn into the air battery together with oxygen, and it deteriorates the air battery. Further, open-type air batteries have a drawback that electrolyte tends to evaporate easily. In view of such drawbacks of air batteries, sealed air batteries have been proposed.
For example, Japanese Patent No. 3764623 describes a sealed oxygen lithium secondary battery having an exterior member in which gas containing pressurized oxygen is enclosed. According to this battery, because the battery is sealed, the moisture in the air does not enter the battery, which enhances the storability of the battery and prolongs the cycle life of the battery. However, such sealed oxygen lithium secondary batteries have the following drawbacks.
That is, because oxygen is produced at the air electrode of the battery upon power charge as is known from the reaction (4) indicated above, if pressurized oxygen is enclosed in the battery case, the oxygen partial pressure in the battery case becomes high, and it makes the reaction (4) less likely to occur, leading to a decrease in the power charge efficiency.
Meanwhile, Published Japanese Translation of PCT application No. 2002-516474 describes a metal/oxygen battery in which oxygen is concentrated using an oxygen concentrator and the obtained high-concentration oxygen is supplied to the negative electrode. According to this technology, in order to provide a high output battery, the concentration of oxygen to be supplied to the battery is controlled in accordance with the target output current of the battery. Further, Japanese Patent Application Publication No. 2003-07357 (JP-A-2003-07357) describes a nonaqueous electrolyte air battery using a nonaqueous electrolyte solution in which carbon oxide is dissolved (claim 3). According to this technology, by dissolving carbon oxide in the nonaqueous electrolyte solution, direct oxidization of the negative electrode is minimized, and therefore the cycle characteristic of the battery improves.